With improvement of technologies like internet, cloud computing, electric vehicles and industrial automation, consumption of electric power becomes greater, which leads to a greater demand for power source. As such, a power conversion device with high power density and high efficiency must be developed. Meanwhile, under the requirements for high power density and high efficiency, the heat dissipation of the power conversion device is also one of the key points that must be considered.
As regards to the power conversion device, it is an effective means of increasing the power density to improve a switch frequency of the internal switching circuit, because when the switch frequency of the switching circuit rises, a size of the filter may correspondingly decrease linearly. Moreover, with the loss unchanged, if the switch frequency of the switching circuit rises, a product of a variation of a flux density borne on the magnetic component, such as, a transformer, etc., within the power conversion device and a working frequency of the magnetic component may rise substantially. As such, a sectional area and the number of turns of the magnetic component may be reduced correspondingly, which makes a volume of the magnetic component is reduced significantly.
The existing power conversion device often comprises a transformer, of which a primary winding is connected to a switching circuit, when the switching circuit is switched on or off, the primary winding of the transformer transmits a received electric energy to a secondary winding, and the electric energy on the secondary winding may be supplied to a load after rectification by a rectifying circuit and filtering by a filter circuit.
However, when the switch frequency of the switching circuit in the existing power conversion device is improved in order to increase a power density, if the switch frequency of the switching circuit has reached a limit that a single transformer can suffer, structure limitation of the single transformer becomes a bottleneck of increasing the power density. Even further, when the power density of the existing power conversion device has to be increased, width and thickness of PCB windings of the single transformer must be increased correspondingly, and it helps little to efficiency improvement of the power conversion device. When the width of the PCB windings of the transformer is increased to a certain degree, it helps little to reduce the winding resistance. When number of the PCB winding layers of the transformer increases further, not only increase of the costs is unacceptable, but also the thermal resistance of the PCB windings of the power conversion device to the top radiator is increased, such that the existing power conversion device is poor in heat dissipation. As can be known, the focus of current research and development is actually how to enable the power conversion device to maintain the overall efficiency and have better heat dissipation under the circumstance of a high power density.
In addition, the magnetic core of the transformer in the existing power conversion device may actually use a E-core or a U-core. All windings of the E-core are centrally wound on a middle column of the E-core, whereas the windings of the U-core are separately wound around two core columns of the U-core on two sides. So when the windings wound on the U-core are PCB windings, a foot print size of the PCB windings may be reduced. Moreover, the PCB windings on the E-core are mostly covered by the E-core and are not exposed to the air, whereas the PCB windings on the U-core are merely partially covered by the U-core, that is, the PCB windings on the U-core are mostly exposed to the air. So the heat dissipation effect of the windings on the U-core is better. Although there are indeed advantages in using the U-core, if the structure of the U-core can be further improved to further reduce loss of the U-core, efficiency of the power conversion device can be improved.
Further, the existing power conversion device must consider the issue of EMI performance. As such, in order to obtain better EMI performance, EMI filters are added to the existing power conversion device. However, this method increases production costs of the power conversion device at the same time.
Therefore, the most urgent subject to be solved at present is to develop a magnetic component which overcomes the above deficiencies, and is capable of reducing core loss while reducing parasitic resistance and thermal resistance of the windings, and a power conversion device using the magnetic component.